Modern wireless communication systems utilize several passive networks for matching and filtering. At radio frequencies (RF), the most critical passive components are inductors and capacitors. The filtering and matching circuits, which include transformers, baluns, filters, diplexers among others, can be fabricated as an integrated passive device (IPD) using silicon, glass, LTCC (Low Temperature Co-fired Ceramic), or other semiconducting substrate and then attached/assembled on the package. Alternatively, such circuits can be fabricated as part of the organic package or PCB (Printed Circuit Board) substrate. Direct fabrication of the passives on the package removes the need for assembly, and can allow package height reduction.
Metal-insulator-metal (MIM) capacitors on package have been demonstrated using high-k material sandwiched between planar metal layers. In this arrangement, the high-k dielectric layer is thinner than the other (build-up) dielectric layers of the package.
However, the density of on-package MIM capacitors have been limited by (1) the electrode surface area that is available, (2) the need for signal escape using vias and associated large via pads.